The cult of Allah promoted by extremists dehumanises and alienates
There are different versions of Islam. The version promoted by extremists dehumanises and alienates, creating an alternative reality. From my point of view, if somebody is Sunni or Shia or whatever else under the umbrella of Islam, the said person is Muslim.
If somebody is Protestant, Catholic or Orthodox or from whichever Christian denomination, the said person is Christian and the same is valid if we are talking about Judaism or any other religion.
For a Muslim to kill Muslims of other denominations within Islam is an abomination as it is an abomination for Christians to kill Christians and for Jews to kill Jews and people of any other religion because I assume that mentally normal individuals value human life and the sacredness of life should be shared by all those who have religious values and by those who do not have religious values because respect for human life should be shared by all.